1. Field of the Invention
The present invention relates to an objective lens barrel for use in cameras such as 35 mm single lens reflex (SLR) camera, motion picture cameras and TV cameras, and more particularly to a lens barrel capable of being automatically and manually controlled to adjust the focus of the objective lens.
2. Description of Prior Art
In prior art Japanese Patent Application laid open under No. 50-151144, an attachment for automatic focus control was proposed, which is driven by an automatic focus control device, and which may be coupled with the focus control ring of a lens barrel. In the case of automatic focus control, the attachment is coupled with the focus control ring for rotating it by the automatic focus control device. The attachment may be disengaged from the focus control ring for allowing the free rotation thereof for manual focus control. Thus, the focus control can be achieved alternatively by manual control means or automatic control means.
In the above mentioned prior art, however, the automatic focus control device is required to have considerable power in order to drive the attachment overcoming the resistance provided in the focus control ring of the lens barrel for preventing undesirable or unexpected movement thereof. Further, the use of such a prior art focus control device results in an inconvenience for manual focus control operation as well as bulkiness, and unshapeliness of the camera since the attachment is to be engaged with the lens barrel on the outside thereof at the focus control ring.